In general, a rotary table includes a clamping structure which allows a pallet base to rotate on a table base and stop rotating at a particular position. A pallet may be mounted on the pallet base, and a workpiece may be mounted on the pallet.
A machine tool cuts the workpiece. In more detail, it is necessary to change a direction of the workpiece so that a cutting tool of the machine tool approaches the workpiece. That is, the rotary table operates to rotate the pallet and the pallet base so that the workpiece is placed in a direction appropriate for the cutting processing.
Meanwhile, a rotational displacement of the rotary table may be numerically controlled by a servo motor, thereby having an ability of precisely dividing an angle. As the ability of dividing an angle is improved, a posture of the pallet base may be changed with a very small angular displacement, such that it is possible to machine the workpiece into a complicated shape. To implement an effect of the ability of dividing an angle, the pallet base needs to be fixed to the table base, and is not to be moved during the cutting processing.
The rotary table has a clamping structure for fixing the pallet base to the table base.
The rotary table and the clamping structure in the related art will be described with reference to the attached FIG. 1. FIG. 1 is a view for explaining the rotary table in the related art.
The rotary table in the related art may include a table base 1, a center shaft 2, a pallet base 3, a joint 4, a clamp 5, and a friction pad 6.
The table base 1 has a worm shaft 1a, and the worm shaft 1a may be operated by a servo motor.
The center shaft 2 may be disposed to stand at a center of the table base 1.
The pallet base 3 is rotatably installed on the center shaft 2. Further, a worm wheel 3a is provided at a lower side of the pallet base 3, and the worm wheel 3a is gear-engaged with the worm shaft 1a. That is, when the worm shaft 1a rotates, the worm wheel 3a rotates, and thus the pallet base 3 may rotate.
The joint 4 is provided between the center shaft 2 and the pallet base 3. Further, the joint 4 enables pressurized oil to be delivered from the center shaft 2 to the pallet base 3.
The clamp 5 is disposed between the table base 1 and the pallet base 3, and fixed to the table base 1. Further, the clamp 5 may be supplied with pressurized oil from the table base 1.
The friction pad 6 is disposed between the clamp 5 and the table base 1, and fixed to the pallet base 3.
When the pressurized oil is provided to the clamp 5, the clamp 5 is expanded, and the friction pad 6 is suppressed. Further, as the friction pad 6 is suppressed, the pallet base 3 is suppressed.
Meanwhile, a bearing unit is provided between the table base 1 and the pallet base 3. The bearing unit enables the pallet base 3 to smoothly rotate on the table base 1.
A configuration of the clamp 5 will be described in more detail with reference to the attached FIGS. 2 and 3. FIGS. 2 and 3 are a perspective view and a cross-sectional view for explaining the clamp on the rotary table in the related art.
The clamp 5 has a ring shaped clamp body 5a, and a flange 5b is formed at a lower side of the clamp body 5a by means of a connecting portion 5d. That is, a chamber 5e is formed by the clamp body 5a, the flange 5b, and the connecting portion 5d. In addition, a flow path 5c is formed in the clamp 5, and the flow path 5c is formed to be connected from the table base 1 to the chamber 5e. 
Meanwhile, a packing may be provided in the chamber 5e, and thus the chamber 5e has a sealed structure. Further, the friction pad 6 may be disposed to be in contact with the flange 5b. 
Therefore, when the pressurized oil is provided to the clamp 5 through the flow path 5c, pressure is formed in the chamber 5e, and the flange 5b suppresses the friction pad 6 by the pressure. As a result, the clamp 5 fixes the pallet base 3 to the table base 1.
However, there is a problem in that the clamp 5 of the rotary table in the related art has low durability, and the friction pad 6 cannot be normally unsuppressed due to seizure. In more detail, there is a problem in that the connecting portion 5d of the clamp 5 is weak. That is, there is a problem in that the connecting portion 5d of the clamp 5 is damaged by pressure formed in the chamber 5e. In addition, there is a problem in that the seizure occurs as the flange 5b of the clamp 5 is stuck to the friction pad 6.